1. Field of the Invention
The present invention relates to the fabrication of semiconductive devices on silicon-on-insulator (SOI) substrates, preferably substrates formed through the separation by implantation of oxygen (SIMOX) process, which are radiation-hard and capable of high voltage operation.
2. Description of the Related Art
Various operating environments for semiconductor devices such as complementary metal-oxide-semiconductor field-effect transistors (CMOS FETs) require that they be resistant to radiation. Exposure to radiation can cause conventional devices to malfunction or destruct.
Radiation hardness may be improved by fabricating devices on SOI substrates. A preferred SOI material is SIMOX, as described in an article entitled "Silicon-on-insulator by oxygen implantation: An advanced technology", by M. Bruel et al, in Microelectronic Engineering 8 (1988), pp. 149-161. The buried insulator layer reduces radiation-induced back channel leakage to a negligible level, and eliminates latch-up paths between adjacent devices which are present in conventional bulk semiconductor substrates.
Although conventional SIMOX devices are essentially free from latch-up, more radiation-hard than devices formed on bulk substrates, and will operate reliably at low voltages, the maximum snap-back voltages are relatively low, on the order of 4 to 7 volts. Snap-back occurs due to an accumulation of charge carriers in doped well regions of a device, and produces a catastrophic increase in current gain resulting in destruction of the device if the operating voltages are increased above the snap-back voltage.